The present invention relates generally to methods and systems for verifying the identity of an individual utilizing spectral data from a non-invasive near-infrared tissue analysis. More specifically, the invention relates to non-invasive methods and apparatus for verifying identity of a living individual using near-infrared absorption of light energy by tissue with identity verified using multivariate discriminant analysis techniques on resulting subcutaneous tissue spectral data as compared to prior stored spectral data for that individual.
Identity verification is useful in many applications. Examples include verifying identity prior to activating machinery or gaining entry to a secure area. Another example would be identity verification of an individual for matching that individual to records on file for that individual, such as for matching hospital patient records when the individual""s identity is unknown. Identity verification is also useful to match police records at the time a suspect is apprehended, but true identity of the suspect is not known. Passwords, keys, numeric codes and fingerprints are solutions currently in use. However, keys and codes can be used by anyone having possession of the keys or codes. A requirement that the person physically at a site be the person authorized to use the key or password is not easily enforced. Fingerprint analysis generally fails to give instant results and security systems relying on fingerprint analysis can be circumvented, as disclosed by Osten et al. in U.S. Pat. No. 5,719,950.
Living human tissue is recognized as a dynamic system containing a multitude of components and analyte information that is particularly useful in the medical profession for diagnosing, treating and monitoring human physical conditions. To this end, effort has been directed toward developing methods for non-invasive measurement of tissue constituents using spectroscopy. The spectrographic analysis of living tissue has been focused on the identification of spectral information that defines individual analytes and relates such spectral data to the analyte""s concentration. Concentrations of these analytes vary with time in an individual patient. Acquiring tissue spectral data with sufficient accuracy for use in diagnosis and treatment has proven difficult. Difficulties in conducting the analysis have been found which are related to the fact that the tissue system is a complex matrix of materials with differing refractive indices and absorption properties. Further, because the constituents of interest are many times present at very low concentrations, high concentration constituents, such as water, have had a detrimental impact on identifying the low level constituent spectral information and giving an accurate reading of the desired constituent concentration. Development of these techniques has always focused on the changes in spectral output with change in concentration of a dynamic analyte of interest, such as glucose. The techniques disclosed are focused on identifying concentrations of specific analytes, the concentration of which is expected to vary with time.
Improved methods and apparatus for gathering and analyzing a near-infrared tissue spectrum for an analyte concentration are disclosed in commonly assigned U.S. patent applications and issued patents. U.S. Pat. No. 5,655,530 and U.S. Pat. No. 5,823,951, filed Apr. 18, 1997, entitled xe2x80x9cMethod for Non-invasive Blood Analyte Measurement with Improved Optical Interfacexe2x80x9d relate to near-infrared analysis of a tissue analyte concentration which varies with time, with a primary focus on glucose concentrations in diabetic individuals. The methods and apparatus include placing a refractive index-matching medium between a sensor and the skin to improve the accuracy and repeatability of testing. U.S. Pat. No. 6,152,876, filed Oct. 19, 1998, entitled xe2x80x9cMethod for Non-Invasive Blood Analyte Measurement with Improved Optical Interfacexe2x80x9d discloses additional improvements in non-invasive living tissue analyte analysis. The disclosure of each of these three applications or patents are hereby incorporated by reference.
U.S. Pat. No. 5,636,633 relates, in part, to another aspect of accurate non-invasive measurement of an analyte concentration. The apparatus includes a device having transparent and reflective quadrants for separating diffuse reflected light from specular reflected light. Incident light projected into the skin results in specular and diffuse reflected light coming back from the skin. Specular reflected light has little or no useful information and is preferably removed prior to collection. U.S. Pat. No. 5,935,062, filed Jun. 9, 1997, entitled xe2x80x9cImproved Diffuse Reflectance Monitoring Apparatusxe2x80x9d, discloses a further improvement for accurate analyte concentration analysis which includes a blocking blade device for separating diffuse reflected light from specular reflected light. The blade allows light from the deeper, inner dermis layer to be captured, rejecting light from the surface, epidermis layer, where the epidermis layer has much less analyte information than the inner dermis layer, and contributes noise. The blade traps specular reflections as well as diffuse reflections from the epidermis. The disclosures of the above patent and application, which are assigned to the assignee of the present application, are also incorporated herein by reference.
U.S. Pat. No. 5,435,309 relates to a system for selecting optimal wavelengths for multivariate spectral analysis. The use of only one wavelength gives insufficient information, especially for solutions having multiple components. The use of too many wavelengths can include too much noise and lead to combinatorial explosion in calculations. Therefore, the number of wavelengths used should be limited and the wavelengths well chosen. Genetic algorithms are used in this reference to select the most fit wavelengths. The disclosure of this patent is incorporated herein by reference.
In contrast to the above discussed prior art techniques for non-invasive analysis of a blood or tissue analyte concentration using infrared spectroscopy, the present invention is based on applicant""s recognition that the resultant tissue spectrum of a particular individual includes unique spectral features and combinations of spectral features which can be used to identify the individual once the analytical device has been trained to identify the individual. Spectral information in the near infrared range is preferred, however, it is recognized that visible or mid-infrared light energy could be used alone or in combination with near infrared. Training of the device is accomplished by use of stored spectral data for that individual from prior testing. Applicants have been able to achieve essentially zero percent false positive error rates with the techniques disclosed herein, even though the tissue being analyzed is a dynamic system with analyte concentrations, and thus, tissue spectral data, varying considerably over time and between analysis. Success of the method of the present invention is believed tied to two components. First, the method incorporates an apparatus and technique for accurately and repeatably acquiring a tissue spectrum which is stable, while remaining sensitive to slight changes in spectral output at any given wave length. The system optimizes optical throughput both into and out of the tissue sample. Second, because the spectral features or combinations of spectral features that are unique for a particular individual are not readily apparent or identified by visual comparison of a spectral result, the present invention relies on discriminant analysis techniques to first train the device to identify spectral features of significance for the individual and then compare such features to new spectral data at the time of attempted verification. The method can incorporate a discriminant analysis technique based upon Mahalanobis distance technique or other distance techniques to compare spectral data acquired from an individual with spectral data present in a database.
The present invention, thus, includes a method for verifying the identity of an individual using non-invasive tissue spectroscopy. A preferred method and apparatus illuminates skin with near-infrared radiation and collects the reflected, non-absorbed near-infrared radiation. Diffuse, rather than specular, reflected light is preferably collected, more preferably light diffusely reflected from the inner dermis rather than the epidermis. The near-infrared spectral data collected can be stored in a computer database. A series of such spectral data are collected from the individual or individuals for which identity verification is desired. The identity of the individual is preferably verified and stored along with the associated spectral data in an authorization database. Authorized spectra can be collected over a period of minutes, or more preferably, a number of spectra can be collected over days and weeks, which allows for adjustment of the individual""s model for verification to account for natural physiological differences at any given time of analysis which will affect a person""s tissue spectra.
After collection, the authorization spectral database for a particular individual can be analyzed, using discriminant analysis tools, relative to new spectral data from an individual purporting to be that individual or an unknown individual. When the purported identity of a target individual is to be verified or an unknown individual""s identity is to be checked against a stored database, a target tissue spectrum can be taken and processed in a manner similar to the processing of the already stored authorization spectra. In one method, the Mahalanobis distance and spectral residual magnitude are used to verify the purported identity or check the unknown individual""s spectral data against a database. In a preferred method, the Mahalanobis distance and spectral residual magnitude are calculated for the target spectrum relative to the database spectra for the individual with the purported identity. Identify is verified only if the aforementioned distance and magnitude are less than a predetermined threshold set for each.
One system for performing identity verification includes: a computer having an input device and an output device; a database including near-infrared tissue spectral data for authorized persons or a collection of spectral data for individuals against which unknown individual""s would be checked; a near-infrared radiation source for projecting near-infrared radiation into subcutaneous tissue; a near-infrared spectrometer for measuring subcutaneous near-infrared intensity over a plurality of wavelengths; and a program running in the computer for discriminating between a target individual""s spectral data and the authorized spectral data or collection of spectra database containing spectra for a group of individuals. The program can include software for performing discriminant analysis. In one system, supervised learning programs can be utilized to assist in associating the various spectral data for each identified individual together.
These and various other advantages and features of novelty which characterize the present invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages, and the object obtained by its use, reference should be made to the drawings which form a further part hereof, and to the accompanying descriptive matter in which there are illustrated and described preferred embodiments of the present invention.